1. Field of the Invention
The present invention relates to image display apparatuses, signal processing apparatuses, image processing methods, and computer program products. More specifically, the present invention relates to an image display apparatus, a signal processing apparatus, an image processing method, and a computer program product with which interlaced-to-progressive (IP) conversion is executed to convert interlaced signals into progressive signals for output to a display.
2. Description of the Related Art
As opposed to CRT displays, which employ dot-sequential impulse driving, flat panel displays (FPDs) implemented by liquid crystal displays (LCDs) or organic electroluminescence (EL) displays employ frame-holding display methods. For example, with a typical frame frequency of 60 Hz, a flat panel display holds the same image during each frame display period ( 1/60 sec=16.7 msec) over the entire display screen.
Most content or broadcasting signals for displaying images are generated in the form of interlaced image data compatible with CRT displays. More specifically, in interlaced image content, each image displayed on the horizontal scanning lines of a CRT display is formed of two fields. First, every other horizontal scanning line is scanned from top to bottom in the first field, and then, every other horizontal scanning line that has not been scanned is scanned from top to bottom in the second field, whereby an image of one frame is displayed.
When such interlaced image content is displayed on a display apparatus that employs a frame-holding display method, such as an LCD, lines carrying display image signals and lines not carrying display image signals occur alternately in each display frame, so that flicker becomes apparent and luminance is reduced to half. In order to solve this problem, interlaced signals are converted into progressive signals, i.e., IP conversion is executed.
As opposed to interlaced scanning, in which every other horizontal scanning line is scanned from the top of the screen, progressive scanning sequentially scans a plurality of horizontal scanning lines (horizontal display lines) forming the screen. The progressive scanning provides image signals of all the lines.
When IP conversion is executed to convert interlaced signals into progressive signals, signals of lines not carrying signals included in the interlaced signals are generated by interpolation. The interlaced signals are converted into progressive signals using the pseudo-signals generated by interpolation, whereby an image corresponding to the progressive signals having signals for all the pixels is displayed. IP conversion is described, for example, in Japanese Unexamined Patent Application Publication No. 8-221039.
However, when IP conversion is executed to convert interlaced signals into progressive signals, pixel values of pixels that do not actually exist are estimated on the basis of spatially or temporally neighboring pixels, so that the original interlaced signals are not reproduced as they are. Thus, a viewer is presented with content altered with pseudo-pixel values. This might be inconvenient for a user wishing for playback of original content as it is.
In this case, in order to check the original content represented by the interlaced image signals, laborious processing arises, such as obtaining interlaced signals before IP conversion and displaying an image corresponding to the interlaced signals on a CRT display.